Method of controlling pressure in a wafer transfer system

ABSTRACT

A wafer transfer system, and method of controlling pressure in the system, includes a loadport for receiving a wafer container, a housing operably connected to the loadport, a wafer transfer mechanism for transferring a wafer between the wafer container and the housing, a wafer container sensor for detecting a presence of the wafer container on the loadport, a variable speed fan disposed in a first portion of the housing, a variable exhaust unit disposed in a second portion of the housing facing the first portion, the variable exhaust unit being capable of varying an exhaust rate of air from the housing, and a controller for variably operating the variable speed fan and the variable exhaust unit in response to a signal from the wafer container sensor.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application based on application Ser. No.10/963,541, filed Oct. 14, 2004 now U.S. Pat. No. 7,438,514, the entirecontents of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer transfer system. Moreparticularly, the present invention relates to a wafer transfer systemfor use in a semiconductor manufacturing process and a method ofcontrolling pressure in the wafer transfer system by varying air flowinto and out of the system.

2. Description of the Related Art

During semiconductor processing, wafers are required to be transferredfrom one location to another location. For example, wafers are requiredto be transferred from a wafer container into process equipment. A wafertransfer system is necessary to perform this transfer. In view of thehigh degree of cleanness that must be provided in semiconductormanufacturing, all areas in the semiconductor manufacturing process towhich the wafers are exposed, including the wafer transfer system, mustbe maintained at a very high level of cleanness.

By effectively maintaining a high degree of cleanness in the wafertransfer system, a processing wafer and a wafer container can avoidinitial contamination or re-contamination by a contaminated wafercontainer or wafer transfer system.

Conventionally, to eliminate contamination during a semiconductormanufacturing process, the manufacturing process was performed in aclean room maintained in a high degree of cleanness and an open typecontainer was used to store and transfer wafers.

In an effort to reduce maintenance costs of the clean room, an equipmentpart of the clean room is selectively maintained in a relatively highdegree of cleanness, while the remainder of the clean room is maintainedin a relatively low degree of cleanness. Accordingly, it is necessary touse a sealed type wafer container to prevent the wafers from becomingcontaminated when the wafers are in an area having a relatively lowdegree of cleanness.

The equipment part of the clean room includes a wafer transfer systemfor transferring wafers into the process equipment from the wafercontainer. The wafer transfer system includes a housing maintainedlocally in a high degree of cleanness. The housing includes a blowingfan in an upper area thereof for blowing clean air downwardly and anexhaust valve in a lower portion thereof for exhausting air.

During a transfer process in the wafer transfer system, particles aregenerated in the housing by operation of a wafer transfer robot. Theseparticles attach in slots in the wafer container due to a flow of airwhen the wafer container is opened or closed. A processed wafer iscontaminated by particles attached onto the slots, and other wafers (notprocessed) are also contaminated in the housing before being transferredinto the process equipment.

One example of particle contamination is nano-sized particles, i.e.,particles having a size on the order of nanometers. Nano-sizedparticles, or nanoparticles, require a high blowing speed of the fan toremove the particles. An amount of electricity consumed by the fanrotating at a high speed in an effort to remove nanoparticles isextremely high. Moreover, when a hole size of a conventional exhaustvalve is not sufficiently large, not all of the nanoparticles aresufficiently exhausted. Resultantly, the nanoparticles accumulateadjacent to the exhaust valve and eventually move up to the top area ofthe housing. This insufficient exhausting results in a “whirlpooleffect” of air and particles in the housing.

Conventional wafer transfer systems have attempted to increase a speedof the blowing fan to remove additional particles in the housing.However, significant electricity is consumed due to the high speed andcontinuous rotation of the blowing fan. In an effort to reduceelectricity consumption, other conventional wafer transfer systems haveoperated a fan at two speeds. However, when a blowing speed of the fanis reduced to conserve energy, sufficient differential pressure betweenthe housing and the clean room may be lost and contamination may enterthe housing.

SUMMARY OF THE INVENTION

The present invention is therefore directed to a wafer transfer systemand method of controlling pressure in the system, which substantiallyovercome one or more of the problems due to the limitations anddisadvantages of the related art.

It is a feature of an embodiment of the present invention to provide awafer transfer system and method of controlling pressure in the wafertransfer system that is capable of reducing electricity consumption.

It is another feature of an embodiment of the present invention toprovide a wafer transfer system and method of controlling pressure inthe wafer transfer system that is capable of removing nano-sizedparticles.

At least one of the above features and other advantages may be providedby a wafer transfer system including a loadport for receiving a wafercontainer, a housing operably connected to the loadport, a wafertransfer mechanism for transferring a wafer between the wafer containerand the housing, a wafer container sensor for detecting a presence ofthe wafer container on the loadport, a variable speed fan disposed in afirst portion of the housing, a variable exhaust unit disposed in asecond portion of the housing facing the first portion, the variableexhaust unit being capable of varying an exhaust rate of air from thehousing, and a controller for variably operating the variable speed fanand the variable exhaust unit in response to a signal from the wafercontainer sensor.

The housing may include an upper surface having an air intake therein, abottom surface, and side surfaces, and a first opening through a sidesurface of the housing, the first opening providing communicationbetween the wafer container and an interior of the housing.

The wafer container may include a door, and the wafer transfer systemmay further include a door assembly for opening and closing the door ofthe wafer container through the first opening.

The wafer transfer mechanism may be a wafer transfer robot.

The first portion may be an upper portion of the housing and the secondportion may be a lower portion of the housing.

The wafer container may be a front open unified port (FOUP). The housingmay be an equipment front end module (EFEM). The door assembly mayinclude a door holder and a transfer arm.

The variable speed fan may be disposed on an interior of the uppersurface of the housing. The wafer transfer system may further include afilter positioned between the variable speed fan and the interior of thehousing. The wafer transfer system may further include a motor foroperating the variable speed fan at varying speeds in response to asignal from the controller. The variable exhaust unit may be disposed onthe bottom surface of the housing.

In a first embodiment of the present invention, the variable exhaustunit may include a first exhaust plate including a plurality of firstopenings and a second exhaust plate including a plurality of secondopenings, the first exhaust plate and the second exhaust plate beingoperable to move relative to one another, thereby aligning ormisaligning the plurality of first openings and the plurality of secondopenings. The variable exhaust unit may further include a guide frame oneither the first or second exhaust plate, the guide frame including agroove on an interior surface thereof for receiving the other of thefirst or second exhaust plate, the guide frame providing for horizontalrelative movement of either the first or the second exhaust plate. Thevariable exhaust unit may further include an operating mechanism to moveeither the first exhaust plate or the second exhaust plate relative tothe other.

Each of the plurality of first and/or second openings may besubstantially circular, and may have a diameter of between about 3-4 cm,or may be substantially rectangular or substantially square, and mayhave a width of between about 3-4 cm. The plurality of first openingsand the plurality of second openings may be each arranged in a pluralityof rows. A distance between each of the plurality of rows may be about3-4 cm.

In a second embodiment of the present invention, the variable exhaustunit may include a first exhaust plate including a plurality of firstopenings, a second exhaust plate including a plurality of secondopenings, and a third exhaust plate including a plurality of thirdopenings, the second exhaust plate being positioned between the firstand third exhaust plates, the second plate being operable to moverelative to the first and third plates, thereby aligning or misaligningthe plurality of first through third openings.

The variable exhaust unit may further include an operating mechanism tomove the second exhaust plate relative to the first and third exhaustplates.

The variable speed fan may operate at a first speed when the wafercontainer sensor fails to detect the presence of the wafer container andat a second speed when the wafer container sensor detects the presenceof the wafer container. The first speed may be lower than the secondspeed. The first speed may produce a blowing speed of about 0.34 m/s.The second speed may produce a blowing speed of about 0.50 m/s.

The variable exhaust unit may be disposed in a first position when thewafer container sensor fails to detect the presence of the wafercontainer and in a second position when the wafer container sensordetects the presence of the wafer container. An exhaust rate in thefirst position may be lower than an exhaust rate in the second position.An exhaust rate in the first position may be about 30% and an exhaustrate in the second position may be between about 50% to 70%.

In the first position, the plurality of first openings and the pluralityof second openings may be misaligned. Alternatively, in the firstposition, the plurality of first openings, the plurality of secondopenings, and the plurality of third openings may be misaligned. In thesecond position, the plurality of first openings and the plurality ofsecond openings may be aligned. Alternatively, in the second position,the plurality of first openings, the plurality of second openings, andthe plurality of third openings may be aligned.

The wafer transfer system may further include a data storage unit forstoring predetermined information regarding a speed of the variablespeed fan and arrangement of the variable exhaust unit in a first stateand a speed of the variable speed fan and arrangement of the variableexhaust unit in a second state, the data storage unit for providing thepredetermined information to the controller.

The wafer transfer system may further include a pressure sensor on thehousing for measuring a pressure of the interior of the housing and apressure of a clean room surrounding the housing, the pressure sensorbeing operable to determine a differential pressure between the interiorof the housing and the clean room.

The wafer transfer system may further include a second opening forproviding communication between the interior of the housing and processequipment.

At least one of the above features and other advantages may be providedby a method of controlling pressure in a wafer transfer system includingmaintaining a housing of the wafer transfer system under a firstpressure, sensing whether a wafer container is present on a loadport,which is operably connected to the housing, varying an interior pressurecondition of the housing from the first pressure to a second pressure,when the wafer container is sensed on the loadport, by operating avariable exhaust unit in the housing to move from a first positionproviding a relatively low rate of exhaust to a second positionproviding a relatively high rate of exhaust, and increasing a speed of avariable speed fan in the housing from a first speed to a second speed,the variable exhaust unit and the variable speed fan facing each other,sensing whether the wafer container is removed from the loadport, andreturning the housing to the first pressure, when the wafer container isremoved from the loadport, by operating the variable exhaust unit tomove from the second position to the first position and decreasing thespeed of the variable speed fan from the second speed to the firstspeed.

The first pressure may be lower than the second pressure.

When the wafer container is absent from the loadport, the wafer transfersystem may be in a first state in which no component of the wafertransfer system is moving and, when the wafer container is disposed onthe loadport, the wafer transfer system may be in a second state inwhich one or more component of the wafer transfer system is moving. Thefirst state may be a static state and the second state may be a dynamicstate.

Operating the variable exhaust unit to move from the first positionproviding the relatively low rate of exhaust to the second positionproviding the relatively high rate of exhaust may include moving eithera first or a second exhaust plate of the variable exhaust unit relativeto the other of the first or second exhaust plate to align a pluralityof first openings in the first exhaust plate with a plurality of secondopenings in the second exhaust plate.

Operating the variable exhaust unit to move from the second positionproviding the relatively high rate of exhaust to the first positionproviding the relatively low rate of exhaust may include moving either afirst or a second exhaust plate of the variable exhaust unit relative tothe other of the first or second exhaust plate to misalign a pluralityof first openings in the first exhaust plate with a plurality of secondopenings in the second exhaust plate.

Operating the variable exhaust unit to move from the first positionproviding the relatively low rate of exhaust to the second positionproviding the relatively high rate of exhaust may include moving asecond exhaust plate of the variable exhaust unit relative to a firstand a third exhaust plate of the variable exhaust unit to align aplurality of second openings in the second exhaust plate with aplurality of first openings in the first exhaust plate and a pluralityof third openings in the third exhaust plate.

Operating the variable exhaust unit to move from the second positionproviding the relatively high rate of exhaust to the first positionproviding the relatively low rate of exhaust may include moving a secondexhaust plate of the variable exhaust unit relative to a first and athird exhaust plate of the variable exhaust unit to misalign a pluralityof second openings in the second exhaust plate with a plurality of firstopenings in the first exhaust plate and a plurality of third openings inthe third exhaust plate.

The method may further include storing predetermined informationregarding the first and second speeds of the variable speed fan andregarding the first and second positions of the variable exhaust unit ina data storing part and providing the predetermined information from thedata storage part to a controller for operating the variable speed fanand the variable exhaust unit.

The method may further include measuring a pressure in the interior ofthe housing and measuring a pressure in a clean room surrounding thehousing using a pressure sensor and determining a differential pressurebetween the interior of the housing and the clean room. Varying theinterior pressure condition of the housing may further include varying aposition of the variable exhaust unit to maintain a predeterminedpressure condition based on the measured differential pressure betweenthe interior of the housing and the surrounding clean room.Alternatively, varying the interior pressure condition of the housingmay further include varying a blowing speed of the variable speed fan tomaintain a predetermined pressure condition based on the measureddifferential pressure between the interior of the housing and thesurrounding clean room.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent to those of ordinary skill in the art bydescribing in detail exemplary embodiments thereof with reference to theattached drawings in which:

FIG. 1 illustrates a sectional view of a wafer transfer system accordingto an embodiment of the present invention, the wafer transfer systembeing disposed in a clean room;

FIG. 2 is a graph of differential pressure versus time;

FIG. 3 is an exemplary plot of particle contamination in a wafercontainer versus frequency of accessing the wafer container, i.e.,opening and closing a door of the wafer container;

FIGS. 4 and 5 are exemplary plots of particle contamination versus timeduring a static state and a dynamic state, respectively;

FIG. 6 is a plot of particle contamination versus blowing speed of a fanduring a dynamic state, in which the transfer robot is operating;

FIG. 7 illustrates a perspective view of a variable exhaust unitaccording to a first embodiment of the present invention;

FIGS. 8A through 8C illustrate a top view of a first exhaust plate, atop view of an alternative first exhaust plate, and a top view ofanother alternative first exhaust plate of the variable exhaust unit asshown in FIG. 7;

FIGS. 9A and 9B illustrate perspective views of alternate configurationsof the variable exhaust unit according to the first embodiment of thepresent invention;

FIGS. 10A and 10B illustrate a perspective view of a variable exhaustunit according to a first embodiment of the present invention in a firstposition and a cross-sectional view, taken along line I-I of FIG. 10A,of the variable exhaust unit according to the first embodiment of thepresent invention in the first position, respectively;

FIGS. 11A and 11B illustrate a perspective view of a variable exhaustunit according to a first embodiment of the present invention in asecond position and a cross-sectional view, taken along line II-II ofFIG. 11A, of the variable exhaust unit according to the first embodimentof the present invention in the second position, respectively;

FIGS. 12A and 12B illustrate a perspective view of a variable exhaustunit according to a second embodiment of the present invention and across-sectional view, taken along line III-III of FIG. 12A, of thevariable exhaust unit according to the second embodiment of the presentinvention in a first position, respectively;

FIG. 13 is a flow chart of a method for adjusting pressure in a housingof the wafer transfer system according to an embodiment of the presentinvention;

FIG. 14 is a flow chart of a method of varying pressure in an interiorof a housing; and

FIG. 15 is a flow chart of another method of varying pressure in aninterior of a housing.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 2004-49456, filed on Jun. 29, 2004, in theKorean Intellectual Property Office, and entitled: “Wafer TransferSystem and Method of Controlling Pressure in the System,” isincorporated by reference herein in its entirety.

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals and characters refer to like elements throughout.

FIG. 1 illustrates a clean room 30, which is used in a semiconductormanufacturing process. The clean room 30 includes a wafer transfersystem 40 according to an embodiment of the present invention, processequipment 10, and a fan filter unit 32, which includes a ceiling blowingfan 32 a and a filter 32 b.

The wafer transfer system 40 includes a loadport 100 for receiving awafer container 20 and a housing 200 operably connected and adjacent tothe loadport 100. The wafer transfer system 40 may be an equipment frontend module (EFEM). The housing 200 is required to be maintained in ahigh degree of cleanness to avoid contaminating and damaging wafers in asemiconductor manufacturing process. The wafer container 20 includes adoor 22 to provide access to wafers contained therein. Further, the door22 prevents an inflow of outside air into the wafer container 20. Thewafer container 20 is air tight and may be a front open unified pod(FOUP). In operation, wafers are transferred from the wafer container 20into the housing 200 by a wafer transfer mechanism, e.g., a wafertransfer robot 280. A wafer container sensor 330 is provided inconnection with the loadport 100 to detect a presence of the wafercontainer 20 on the loadport 100.

FIG. 2 is a graph of differential pressure versus time, which shows apressure difference between the interior of the housing 200 and theinterior of the wafer container 20 when the wafer container 20 is openedor closed to provide access to the wafers.

In FIG. 2, the dotted line represents a variation in pressure when thewafer container is opened and the solid line represents a variation inpressure when the wafer container is closed. Referring to region ‘a’,when the wafer container is opened, an interior pressure of the wafercontainer decreases to that of the housing, and then due to thispressure difference, air flows into the wafer container from thehousing. Referring to region ‘b’, when the wafer container is closed,air flows into the wafer container from the housing, and the interiorpressure of the wafer container increases.

Due to this pressure difference resulting from the opening and closingof the wafer container door, a particle from the housing may enter thewafer container.

FIG. 3 is an exemplary plot of particle contamination in the wafercontainer versus frequency of accessing the wafer container, i.e.,opening and closing the wafer container. In FIG. 3, a first plotrepresents a top slot (slot #25) in the wafer container and a secondplot represents a bottom slot (slot #1) in the wafer container. As maybe seen in FIG. 3, when the wafer container door is first opened at atop area thereof, a relatively large number of particles are detected inthe top slot (slot #25) of the wafer container, and a relatively fewernumber of particles are detected in the bottom slot (slot #1). Further,it may be seen that as the wafer container repeatedly accessed, thenumber of particles therein increases, especially at the top slot, viz.,slot #25.

Referring back to FIG. 1, the housing 200 includes an upper surfacehaving an air intake 260, a bottom surface, a first side surface 220,and a second side surface 240. Air from the clean room 30, whichsurrounds the wafer transfer system 40, is able to enter the housing 200through the air intake 260. The first side surface 220 of the housing200 includes a first opening, i.e., a first wafer transfer pathway 222,between the housing 200 and the wafer container 20. The first wafertransfer pathway 222 provides communication between the wafer container20 and an interior of the housing 200. The second side surface 240 ofthe housing 200 includes a second opening, i.e., a second wafer transferpathway 242, between the housing 200 and the process equipment 10.

The wafer transfer system 40 includes a door assembly 290 for openingand closing the door 22 of the wafer container 20 through the firstwafer transfer pathway 222. The door assembly 290 may include a doorholder 292 for detaching the door 22 from the wafer container 20 and atransfer arm 294 for operating the door holder 292.

The housing 200 further includes a pressure adjusting unit 300 forvarying a degree of cleanness in the housing 200. The pressure adjustingunit 300 includes a variable speed fan-filter unit 320, a variableexhaust unit 340, and a controller 360. The variable speed fan-filterunit 320, which may be disposed in an upper portion of the housing 200,includes a variable speed fan 322 and a filter 324 for removingparticles from air flowing into the housing 200. The variable speed fan322 may be disposed on an interior of the upper surface of the housing200. The filter 324 may be positioned between the variable speed fan 322and the interior of the housing 200. A motor 326 operates the variablespeed fan 322 at varying speeds in response to a signal from thecontroller 360.

The variable exhaust unit 340, which may be disposed in a lower portionof the housing 200, includes a first exhaust plate 342, a second exhaustplate 344, and an operating mechanism 348 for moving one of the first orsecond exhaust plates 342, 344 to vary an exhaust rate of the variableexhaust unit 340. The variable exhaust unit 340 may be disposed on thebottom surface of the housing 200. The controller 360 variably operatesthe variable speed fan 322 and the variable exhaust unit 340 in responseto a signal from the wafer container sensor 330. The controller 360 isable to control pressure in the housing 200 by varying a speed ofrevolution of the variable speed fan 322 and an exhaust rate of thevariable exhaust unit 340.

The wafer transfer system 40 operates in two states, viz., a staticstate and a dynamic state. During operations, the pressure adjustingunit 300 varies a degree of cleanness in the housing 200 by varyingpressure in the housing 200 based on whether the wafer transfer system40 is in the static state or the dynamic state. In the static state, nooperations are occurring and no parts are moving. In the dynamic state,operations are in progress and parts are moving, e.g., the door assembly290 is opening or closing the door 22 of the wafer container 20 or thewafer transfer robot 280 is engaging wafers to either load or unload thewafer container 20 or the process equipment 10.

FIGS. 4 and 5 are exemplary plots of particle contamination versus timeduring the static state and the dynamic state, respectively. FIGS. 4 and5 show an amount of particles in the housing 200 according to whetherthe transfer process is in progress in the wafer transfer system 40.When the transfer process is not in progress, i.e., the wafer transfersystem 40 is in the static state, the transfer robot 280 in the housing200 is not moving. Accordingly, virtually no particles are detected inthe housing 200 during the static state, as shown FIG. 4. In FIG. 5,however, when the transfer process is in progress, the transfer robot280 in the housing 200 is moving. Accordingly, a large number ofparticles are detected in the housing 200, as shown in FIG. 5, due tothe mechanical operation of the transfer robot 280. In FIG. 5, inconnection with the dynamic state, the variable speed fan 322 is blowingat a conventional speed of 0.34 m/s and the measured particles have asize of greater than 0.1 μm. A conventional blowing speed of 0.34 m/s isused to emphasize a difference in particle contamination between thestatic state and the dynamic state. As will be discussed in greaterdetail below, in the present invention, a blowing speed of greater than0.34 m/s is used in the dynamic state, which reduces particlecontamination in the dynamic state. In the context of the presentinvention, blowing speed represents the speed at which air moves awayfrom the variable speed fan 322.

Accordingly, when the wafer transfer system 40 is in the dynamic state,the interior of the housing 200 is required to be maintained in a higherdegree of cleanness, as compared to the static state. This higher degreeof cleanness may be obtained by increasing the blowing speed of thevariable speed fan 322 and increasing an exhaust rate of the variableexhaust unit 340. When the wafer transfer system 40 is in the staticstate, the interior of the housing 200 may be maintained in a relativelylower degree of the cleanness. This relatively lower degree of thecleanness may be obtained by decreasing the blowing speed of thevariable speed fan 322 and decreasing the exhaust rate of the variableexhaust unit 340.

FIG. 6 is a plot of particle contamination versus blowing speed of thefan during the dynamic state in which the transfer robot is operating.More specifically, FIG. 6 shows an effect of the speed of the air in thehousing on a degree of the cleanness in the housing, i.e., a level ofparticle contamination.

As shown in FIG. 6, as the blowing speed increases, an amount ofparticles decreases. Specifically, in region ‘a’, a blowing speed is setat 0.34 m/s, in region ‘b’ a blowing speed is set at 0.44 m/s, and inregion ‘c’, a blowing speed is set at 0.50 m/s. A blowing speed of 0.44m/s is necessary to remove microparticles and a blowing speed of 0.50m/s is necessary to remove nanoparticles.

It is not practical, however, to maintain a blowing speed of 0.50 m/s atall times in view of the attendant consumption of electricity. Moreover,simply reducing the blowing speed at certain times results in a loss ofsufficient differential pressure and an increase in contamination in thehousing. Sufficient differential pressure must be maintained to preventparticle contamination from entering the housing from the surroundingclean room.

Because it is important to maintain a positive differential pressurebetween the interior of the housing 200 and the surrounding clean room30, it is not sufficient to vary only the blowing speed of the variablespeed fan 322. An exhaust rate must be correspondingly varied. Forexample, if the fan speed is too fast and the exhaust rate is too low,air is not exhausted fast enough, thereby re-circulating up from thebottom of the housing 200 and causing a “whirlpool effect.” Further,this situation is not able to eliminate nanoparticles. If the fanblowing speed is too slow and the exhaust rate is too high, a positivedifferential pressure between the interior of the housing 200 and thesurrounding clean room 30 is not maintained, so that contamination isable to enter the housing 200. Accordingly, in the wafer transfer system40 according to an embodiment of the present invention, as the fanblowing speed increases to increase a cleanness of the housing 200, theexhaust rate correspondingly increases to eliminate nanoparticles.Conversely, as the fan blowing speed decreases to conserve energy, theexhaust rate correspondingly decreases, thereby maintaining sufficientdifferential pressure to avoid contamination of the housing 200.

In operation, the variable speed fan 322 operates at a first speed toproduce a first blowing speed when the wafer container sensor 330 failsto detect the presence of the wafer container 20, i.e., the wafertransfer system 40 is in the static state, and at a second speed toproduce a second blowing speed when the wafer container sensor 330detects the presence of the wafer container 20, i.e., the wafer transfersystem 40 is in the dynamic state. The first speed, which may produce ablowing speed of about 0.34 m/s is lower than the second speed, whichmay produce a blowing speed of about 0.50 m/s.

Correspondingly, the variable exhaust unit 340 is disposed in a firstposition when the wafer container sensor 330 fails to detect thepresence of the wafer container 20 (static state) and in a secondposition when the wafer container sensor 330 detects the presence of thewafer container 20 (dynamic state). An exhaust rate in the firstposition, which may be about 30%, is lower than an exhaust rate in thesecond position, which may be between about 50% to 70%. The exhaust rateis calculated by dividing a total area of the openings through which airmay pass by a total area of an exhaust plate supporting the openings.The first and second positions of the variable exhaust unit 340 will bedescribed below in connection with FIGS. 10A-11B.

Referring back to FIG. 1, the wafer transfer system 40 may furtherinclude a data storage unit 362 for storing predetermined informationregarding a blowing speed of the variable speed fan 322 and anarrangement of the variable exhaust unit 340 in a first state, i.e., thestatic state, and a blowing speed of the variable speed fan 322 and anarrangement of the variable exhaust unit 340 in a second state, i.e.,the dynamic state. The data storage unit 362 improves an efficiency ofthe wafer transfer system 40 by providing the predetermined informationto the controller 360.

The wafer transfer system may further include a pressure sensor 350 onthe housing 200 for measuring a pressure of the interior of the housing200 and a pressure of the clean room 30 surrounding the housing 200. Thepressure sensor 350 is operable to determine a differential pressurebetween the interior of the housing 200 and the clean room 30.

The wafer transfer system 40 according to an embodiment of the presentinvention is able to maintain a predetermined differential pressurebetween the interior of the housing 200 and the clean room 30. Morespecifically, the wafer transfer system 40 is able to vary a blowingspeed of the variable speed fan 322 or an exhaust rate of the variableexhaust unit 340 in order to maintain a predetermined pressurecondition.

FIG. 7 illustrates the variable exhaust unit 340 according to a firstembodiment of the present invention. FIGS. 8A through 8C illustrate topviews of the first exhaust plate 342, an alternative first exhaust plate342′, and another alternative first exhaust plate 342″, respectively, ofthe variable exhaust unit 340 shown in FIG. 7.

The variable exhaust unit 340 includes the first exhaust plate 342 andthe second exhaust plate 344 separated by a predetermined distance, e.g.about 1 cm. The first exhaust plate 342 includes a plurality of firstopenings 342 a, which acts as a first exhaust route. The second exhaustplate 344 includes a plurality of second openings 344 a, which acts as asecond exhaust route. The plurality of first and second openings 342 aand 344 a may be substantially circular, as depicted in FIG. 8A.Alternatively, the variable exhaust unit 340 may include a plurality ofsubstantially rectangular first openings 342 a′ in the alternative firstexhaust plate 342′, as depicted in FIG. 8B. In yet another alternative,the variable exhaust unit 340 may include a plurality of substantiallysquare first openings 342 a″ in the another alternative first exhaustplate 342″, as depicted in FIG. 8C. The variable exhaust unit 340 mayalso include a plurality of substantially rectangular second openings344 a′ in an alternative second exhaust plate 344′. When the pluralityof first or second openings 342 a and 344 a are substantially circular,each may have a diameter of between about 3-4 cm. When the plurality offirst or second openings are substantially rectangular or square, e.g.,second openings 344 a′, each may have a width of between about 3-4 cm.Each of the plurality of first and second openings may have the samediameter or width. Further, the plurality of first and second openingsmay be formed in a plurality of rows and columns. Each of the rows andcolumns may have a predetermined distance therebetween, e.g., about 3-4cm.

The second exhaust plate 344 may further include a guide frame 345 forconducting the horizontal movement of the second exhaust plate 344. Aninner wall of the guide frame 345 has a groove 345 a for receiving anedge of the second exhaust plate 344. The second exhaust plate 344 movesbetween the first position and the second position along the groove 345a of the guide frame 345. The second exhaust plate 344 is operated bythe operating mechanism 348. As described above, the controller 360adjusts the movement of the second exhaust plate 344 by controlling theoperating mechanism 348. Although in an exemplary embodiment of thepresent invention, the second exhaust plate 344 is described as beingmoved by the operating mechanism 348 relative to the first exhaust plate342, in an alternative arrangement, the operating mechanism 348 maycontrol the first exhaust plate 342 to move relative to the secondexhaust plate 344. In that arrangement, the guide frame 345 may bealternatively disposed on the first exhaust plate 342.

FIGS. 9A and 9B illustrate alternative embodiments of the variableexhaust unit 340 according to the first embodiment of the presentinvention.

As may be seen in FIGS. 9A and 9B, the plurality of first and/or secondopenings 342 a′ or 344 a′ may be substantially rectangular. In thisarrangement, each of the plurality of first and second openings may havea width of between about 3-4 cm. Further, the plurality of first andsecond openings 342 a′ and 344 a′ may be each arranged in a plurality ofrows. In this case, a distance between each of the plurality of rows isabout 3-4 cm.

As described above, the variable exhaust unit 340 may be disposed in thefirst position or the second position. In the first position, whichprovides a relatively low rate of exhaust, the plurality of firstopenings 342 a and the plurality of second openings 344 a aremisaligned. In the second position, which provides a relatively highrate of exhaust, the plurality of first openings 342 a and the pluralityof second openings 344 a are aligned.

More specifically, FIG. 10A illustrates the first and second exhaustplates 342 and 344 of the variable exhaust unit 340 as shown in FIG. 7in the first position, wherein the plurality of first openings 342 a andthe plurality of second openings 344 a are misaligned. FIG. 10Billustrates a cross-sectional view of the first and second exhaustplates 342 and 344 of the variable exhaust unit 340 of FIG. 10A takenalong line I-I in the first position. FIG. 11A illustrates the first andsecond exhaust plates 342 and 344 of the variable exhaust unit 340 asshown in FIG. 7 in the second position, wherein the plurality of firstopenings 342 a and the plurality of second openings 344 a are aligned.FIG. 11B illustrates a cross-sectional view of the first and secondexhaust plates 342 and 344 of the variable exhaust unit 340 of FIG. 11Ataken along line II-II in the second position.

In FIGS. 10B and 11B, dotted lines show a direction of airflow exhaustedthrough the first and second exhaust plates 342, 344. As shown in FIG.10B, if the second exhaust plate 344 moves to the first position in thestatic state, the exhaust of air is not achieved smoothly from thehousing 200 because the flow direction of the air exhausted out of thevariable exhaust unit 340 deviates from the flow direction of the airexiting the housing 200.

As shown in FIG. 11B, if the second exhaust plate 344 moves to thesecond position in the dynamic state, the exhaust of the air can beachieved smoothly from the housing 200 because the flow direction of theair exhausted out of the variable exhaust unit 340 is the same as theflow direction of the air exiting the housing 200.

Further, the smaller the particle size to be removed from the housing200, the greater an overlap between the plurality of first openings 342a and the plurality of second openings 344 a. As the overlap between theplurality of first openings 342 a and the plurality of second openings344 a increases, the exhaust rate through the variable exhaust unit 340increases.

FIG. 12A illustrates a variable exhaust unit 340′ according to a secondembodiment of the present invention. FIG. 12B illustrates across-sectional view of the variable exhaust unit of FIG. 12A takenalong line III-III in the first position, wherein a plurality of firstopenings, a plurality of second openings and a plurality of thirdopenings are misaligned.

The variable exhaust unit 340′ according to the second embodiment of thepresent invention further includes a third exhaust plate 346 having aplurality of third openings 346 a, which acts as a third exhaust route.In this arrangement, the first and third exhaust plates 342, 346 arefixed and the second exhaust plate 344, which is disposed therebetween,is operable to move horizontally. The first and second exhaust plates342 and 344 and the second and third exhaust plates 344 and 346 may bespaced apart by a predetermined distance, e.g., about 1 cm. The thirdexhaust plate 346 may have substantially the same shape as the firstexhaust plate 342. The size and shape of each of the plurality of thirdopenings 346 a may be substantially the same or may be different fromthe size and shape of each of the plurality of first openings 342 a.

In the second embodiment, the second exhaust plate 344 includes theguide frame 345. In operation, the plurality of third openings 346 a maybe fixedly aligned with the plurality of first openings 342 a, and theoperating mechanism (not shown) moves the second exhaust plate 344horizontally between the first and third exhaust plates 342 and 346 soas to align or misalign the plurality of second openings 344 a in thesecond exhaust plate 344 with the plurality of first and third openings342 a and 346 a.

As shown in FIG. 12B, due to the third exhaust plate 346, air exhaustionmay be substantially reduced in the first position because of themultiple deviations in the direction of the air flow. Accordingly, inthe static state, exhaustion of air from the housing may be virtuallyprevented.

FIG. 13 is a flow chart of a method for adjusting pressure in thehousing 200 of the wafer transfer system 40. In step S10, an initialpressure of an interior of the housing 200 is maintained at a firstpressure condition, which corresponds to the static state. Because thestatic state is the default state for the wafer transfer system 40, thefirst pressure condition, which corresponds to the static state, is thedefault pressure condition.

In step S20, the wafer container sensor 330 continuously checks for thepresence of the wafer container 20 on the loadport 100. The result ofthis check is transferred to the controller 360. Until the controller360 receives a loading signal from the wafer container sensor 330indicating the presence of the wafer container 20, the controller 360continuously maintains the interior of the housing 200 at the firstpressure condition, corresponding to the static state. When thecontroller 360 receives the loading signal, i.e., the wafer container 20is present on the loadport 100, the controller 360 recognizes the wafertransfer system 40 has entered the dynamic state.

In step S30, the pressure in the interior of the housing 200 is elevatedto a second pressure condition, which corresponds to the dynamic state.To elevate the pressure of the interior of the housing 200 to the secondpressure condition corresponding to the dynamic state, the controller360 signals the second exhaust plate 344 to move to the second positionand signals the variable speed fan 322 to increase the blowing speedthereof.

In step S40, the interior of the housing 200 is continuously maintainedat the second pressure condition corresponding to the dynamic state.

In step S50, operations of the wafer transfer system 40 proceed. Inparticular, the door assembly 290 opens the wafer container 20 and awafer is transferred from the wafer container 20 through the housing 200and into the process equipment 10 by the wafer transfer robot 280. Afterthe process is completed, the wafer is transferred from the processequipment 10, back through the housing 200, and into the wafer container20 by the robot 280. Subsequently, the wafer container 20 is closed bythe door assembly 290, and the wafer container 20 is removed from theloadport 100. Because the wafer container sensor 330 continuously checksfor the presence of the wafer container 20 on the loadport 100, when thewafer container 20 is removed, the wafer container sensor 330 transfersan unloading signal to the controller 360 to indicate the absence of thewafer container 20 from the loadport 100 and the return of the wafertransfer system 40 to the static state.

In step S60, until the controller 360 receives the unloading signalindicating that the wafer container 20 has been removed from theloadport 100, the controller 360 continuously maintains the interior ofthe housing 200 at the second pressure condition corresponding to thedynamic state. When the controller 360 receives the unloading signal,the controller 360 recognizes that the wafer transfer system 40 hasreturned to the static state, and the controller 360 sends a signal tothe variable speed fan 322 and the variable exhaust unit 340 to reducethe pressure in the interior of the housing 200 back to the firstpressure condition corresponding to the static state. To accomplish thispressure change, the controller 360 signals the variable exhaust unit340 to move the second exhaust plate 344 back to the first position andsignals the variable speed fan 322 to reduce the blowing speed thereof.

The method then returns to step S10, in which the interior of thehousing 200 is continuously maintained at the first pressure conditioncorresponding to the static state.

FIGS. 14 and 15 are flow charts for explaining methods of varyingpressure in the interior of the housing 200 in response to adifferential pressure between the interior of the housing 200 and thesurrounding clean room 30.

Referring to FIG. 14, in step S120, the wafer container sensor 330determines whether the wafer container 20 is present on the loadport100. Step S120 may additionally include the data storage unit 362storing set points of the pressure conditions and the positions of thevariable exhaust unit 340 corresponding to both the static state and thedynamic state of the wafer transfer system 40. The data storage unit 362may then provide the predetermined information to the controller 360 tocontrol the variable exhaust unit 340.

In step S140, the variable exhaust unit 340 is positioned in either thefirst position providing a relatively low rate of exhaust or the secondposition providing a relatively high rate of exhaust depending onwhether the wafer container 20 is absent from or present on the loadport100, respectively.

In the variable exhaust unit 340 according to the first embodiment ofthe present invention, operating the variable exhaust unit 340 to movefrom the first position to the second position may include moving eitherthe first or second exhaust plate 342, 344 of the variable exhaust unit340 relative to the other of the first or second exhaust plate 342, 344to align the plurality of first openings 342 a in the first exhaustplate 342 with the plurality of second openings 344 a in the secondexhaust plate 344. Operating the variable exhaust unit 340 to move fromthe second position to the first position may include moving either thefirst or a second exhaust plate 342, 344 of the variable exhaust unit340 relative to the other of the first or second exhaust plate 342, 344to misalign the plurality of first openings 342 a in the first exhaustplate 342 with the plurality of second openings 344 a in the secondexhaust plate 344.

In the variable exhaust unit 340′ according to the second embodiment ofthe present invention, operating the variable exhaust unit to move fromthe first position to the second position may include moving the secondexhaust plate 344 of the variable exhaust unit 340′ relative to thefirst and third exhaust plates 342, 346 to align the plurality of secondopenings 344 a in the second exhaust plate 344 with the plurality offirst openings 342 a in the first exhaust plate 342 and the plurality ofthird openings 346 a in the third exhaust plate 346. Operating thevariable exhaust unit 340′ to move from the second position to the firstposition may include moving the second exhaust plate 344 of the variableexhaust unit 340′ relative to the first and third exhaust plates 342,346 to misalign the plurality of second openings 344 a in the secondexhaust plate 344 with the plurality of first openings 342 a in thefirst exhaust plate 342 and the plurality of third openings 346 a in thethird exhaust plate 346.

In step S160, a pressure in the housing 200 and a pressure in thesurrounding clean room 30 are measured by the pressure measurer 350 andthe pressure difference between the interior and the exterior of thehousing 200 is calculated.

In step S180, a blowing speed of the variable speed fan 322 is varied tomaintain the interior of the housing 200 in either the first pressurecondition or the second pressure condition, depending on whether thewafer container 20 is absent from or present on the loadport 100,respectively.

Referring now to FIG. 15, in step S220, the wafer container sensor 330detects the presence of the wafer container 20 on the loadport 100. StepS220 may additionally include the data storage unit 362 storing setpoints of the pressure conditions and the blowing speed of the variablespeed fan 322 corresponding to both the static state and the dynamicstate of the wafer transfer system 40. The data storage unit 362 maythen provide the predetermined information to the controller 360 tocontrol the variable speed fan 322.

In step S240, the variable speed fan 322 is rotated at either the firstspeed or the second speed depending on whether wafer container 20 isabsent from or present on the loadport 100, respectively.

In step S260, a pressure in the housing 200 and a pressure in thesurrounding clean room 30 are measured by the pressure measurer 350 andthe pressure difference between the interior and the exterior of thehousing 200 is calculated.

In step S280, the position of the variable exhaust unit 340 is varied toto maintain the interior of the housing in either the first pressurecondition or the second pressure condition, depending on whether thewafer container is absent from or present on the loadport 100,respectively.

In conclusion, controlling the pressure within the housing of the wafertransfer system, and resultantly a differential pressure between theinterior and exterior of the housing, depends on the blowing speed ofthe variable speed fan and the exhaust rate of the variable exhaustunit, which is determined by an amount of overlap of the first andsecond exhaust plates or the first, second, and third exhaust plates. Inthe static state, the blowing speed of the variable speed fan isrelatively lower and the exhaust rate of the variable exhaust unit isrelatively lower to reduce electricity consumption while maintaining asufficient pressure difference. In the dynamic state, the blowing speedof the variable speed fan is relatively higher and the exhaust rate ofthe variable exhaust unit is relatively higher to increase an amount ofparticle contamination removed from the housing while sufficientmaintaining a sufficient pressure difference.

As may be seen from the above description, a wafer transfer system andmethod of controlling pressure in the wafer transfer system according toan embodiment of the present invention is able to increase or decrease ablowing speed of a variable speed fan and correspondingly increase ordecrease an exhaust rate of a variable exhaust unit to increase a levelof cleanness in the wafer transfer system by reducing a particleresidence time in the housing or to reduce electricity consumption ofthe wafer transfer system, while maintaining a sufficient differentialpressure between the interior of the wafer transfer system and thesurrounding clean room to prevent contamination of the interior of thehousing.

Exemplary embodiments of the present invention have been disclosedherein and, although specific terms are employed, they are used and areto be interpreted in a generic and descriptive sense only and not forpurpose of limitation. Accordingly, it will be understood by those ofordinary skill in the art that various changes in form and details maybe made without departing from the spirit and scope of the presentinvention as set forth in the following claims.

What is claimed is:
 1. A method of controlling pressure in a wafertransfer system, the method comprising: maintaining a housing of thewafer transfer system under a first pressure; sensing whether a wafercontainer is present on a loadport, which is operably connected to thehousing; varying an interior pressure condition of the housing from thefirst pressure to a second pressure, when the wafer container is sensedon the loadport, by operating a variable exhaust unit in the housing tomove from a first position providing a relatively low rate of exhaust toa second position providing a relatively high rate of exhaust, andincreasing a speed of a variable speed fan in the housing from a firstspeed to a second speed, the variable exhaust unit and the variablespeed fan facing each other; sensing whether the wafer container isremoved from the loadport; and returning the housing to the firstpressure, when the wafer container is removed from the loadport, byoperating the variable exhaust unit to move from the second position tothe first position and decreasing the speed of the variable speed fanfrom the second speed to the first speed, wherein the first pressure andthe second pressure are greater than a pressure in a clean roomsurrounding the housing.
 2. The method of controlling pressure in awafer transfer system as claimed in claim 1, wherein the first pressureis lower than the second pressure.
 3. The method of controlling pressurein a wafer transfer system as claimed in claim 1, wherein, when thewafer container is absent from the loadport, the wafer transfer systemis in a first state in which no component of the wafer transfer systemis moving and, when the wafer container is disposed on the loadport, thewafer transfer system is in a second state in which one or morecomponent of the wafer transfer system is moving.
 4. The method ofcontrolling pressure in a wafer transfer system as claimed in claim 3,wherein the first state is a static state.
 5. The method of controllingpressure in a wafer transfer system as claimed in claim 3, wherein thesecond state is a dynamic state.
 6. The method of controlling pressurein a wafer transfer system as claimed in claim 1, wherein operating thevariable exhaust unit to move from the first position providing therelatively low rate of exhaust to the second position providing therelatively high rate of exhaust comprises: moving either a first or asecond exhaust plate of the variable exhaust unit relative to the otherof the first or second exhaust plate to align a plurality of firstopenings in the first exhaust plate with a plurality of second openingsin the second exhaust plate.
 7. The method of controlling pressure in awafer transfer system as claimed in claim 1, wherein operating thevariable exhaust unit to move from the second position providing therelatively high rate of exhaust to the first position providing therelatively low rate of exhaust comprises: moving either a first or asecond exhaust plate of the variable exhaust unit relative to the otherof the first or second exhaust plate to misalign a plurality of firstopenings in the first exhaust plate with a plurality of second openingsin the second exhaust plate.
 8. The method of controlling pressure in awafer transfer system as claimed in claim 1, wherein operating thevariable exhaust unit to move from the first position providing therelatively low rate of exhaust to the second position providing therelatively high rate of exhaust comprises: moving a second exhaust plateof the variable exhaust unit relative to a first and a third exhaustplate of the variable exhaust unit to align or misalign a plurality ofsecond openings in the second exhaust plate with a plurality of firstopenings in the first exhaust plate and a plurality of third openings inthe third exhaust plate.
 9. The method of controlling pressure in awafer transfer system as claimed in claim 1, wherein operating thevariable exhaust unit to move from the second position providing therelatively high rate of exhaust to the first position providing therelatively low rate of exhaust comprises: moving a second exhaust plateof the variable exhaust unit relative to a first and a third exhaustplate of the variable exhaust unit to misalign or align a plurality ofsecond openings in the second exhaust plate with a plurality of firstopenings in the first exhaust plate and a plurality of third openings inthe third exhaust plate.
 10. The method of controlling pressure in awafer transfer system as claimed in claim 1, further comprising:providing predetermined information regarding the first and secondspeeds of the variable speed fan and regarding the first and secondpositions of the variable exhaust unit from a data storage part to acontroller for operating the variable speed fan and the variable exhaustunit.
 11. The method of controlling pressure in a wafer transfer systemas claimed in claim 1, further comprising: measuring a pressure in theinterior of the housing and measuring a pressure in the clean roomsurrounding the housing using a pressure sensor; and determining adifferential pressure between the interior of the housing and the cleanroom.
 12. The method of controlling pressure in a wafer transfer systemas claimed in claim 11, wherein varying the interior pressure conditionof the housing further comprises: varying a position of the variableexhaust unit to maintain a predetermined pressure condition based on themeasured differential pressure between the interior of the housing andthe surrounding clean room.
 13. The method of controlling pressure in awafer transfer system as claimed in claim 11, wherein varying theinterior pressure condition of the housing further comprises: varying ablowing speed of the variable speed fan to maintain a predeterminedpressure condition based on the measured differential pressure betweenthe interior of the housing and the surrounding clean room.
 14. A methodof controlling pressure in a wafer transfer system, comprising:maintaining a housing of the wafer transfer system under a firstpressure; sensing whether a wafer container is present on a loadport,which is operably connected to the housing; varying an interior pressurecondition of the housing from the first pressure to a second pressure,when the wafer container is sensed on the loadport, by operating avariable exhaust unit in the housing to move from a first positionproviding a relatively low rate of exhaust to a second positionproviding a relatively high rate of exhaust, sensing whether the wafercontainer is removed from the loadport; and returning the housing to thefirst pressure, when the wafer container is removed from the loadport,by operating the variable exhaust unit to move from the second positionto the first position, wherein operating the variable exhaust includesmoving a second exhaust plate of the variable exhaust unit relative to afirst and a third exhaust plate of the variable exhaust unit to align ormisalign a plurality of second openings in the second exhaust plate witha plurality of first openings in the first exhaust plate and a pluralityof third openings in the third exhaust plate.
 15. The method ofcontrolling pressure in a wafer transfer system as claimed in claim 14,further comprising: measuring a pressure in the interior of the housingand measuring a pressure in a clean room surrounding the housing using apressure sensor; and determining a differential pressure between theinterior of the housing and the clean room.
 16. The method ofcontrolling pressure in a wafer transfer system as claimed in claim 14,wherein varying the interior pressure condition of the housing furthercomprises: varying a position of the variable exhaust unit to maintain apredetermined pressure condition based on the measured differentialpressure between the interior of the housing and the surrounding cleanroom.
 17. A method of controlling pressure in a wafer transfer system,the method comprising: maintaining a housing of the wafer transfersystem under a first pressure; sensing whether a wafer container ispresent on a loadport, which is operably connected to the housing;varying an interior pressure condition of the housing from the firstpressure to a second pressure, when the wafer container is sensed on theloadport, by operating a variable exhaust unit in the housing to movefrom a first position providing a relatively low rate of exhaust to asecond position providing a relatively high rate of exhaust, andincreasing a speed of a variable speed fan in the housing from a firstspeed to a second speed, the variable exhaust unit and the variablespeed fan facing each other; sensing whether the wafer container isremoved from the loadport; and returning the housing to the firstpressure, when the wafer container is removed from the loadport, byoperating the variable exhaust unit to move from the second position tothe first position and decreasing the speed of the variable speed fanfrom the second speed to the first speed, wherein, when the wafercontainer is absent from the loadport, the wafer transfer system is in afirst state in which no component of the wafer transfer system is movingand, when the wafer container is disposed on the loadport, the wafertransfer system is in a second state in which one or more component ofthe wafer transfer system is moving.
 18. The method of controllingpressure in a wafer transfer system as claimed in claim 17, wherein thefirst state is a static state.
 19. The method of controlling pressure ina wafer transfer system as claimed in claim 17, wherein the second stateis a dynamic state.